block: restore a specific error code in bdev_del_partition

mdadm relies on the fact that deleting an invalid partition returns
-ENXIO or -ENOTTY to detect if a block device is a partition or a
whole device.

Fixes: 08fc1ab ("block: fix locking in bdev_del_partition")
Reported-by: kernel test robot <rong.a.chen@intel.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Author: Christoph Hellwig

block/partitions/core.c

@@ -537,7 +537,7 @@ int bdev_del_partition(struct block_device *bdev, int partno)
 
 	bdevp = bdget_disk(bdev->bd_disk, partno);
 	if (!bdevp)
-		return -ENOMEM;
+		return -ENXIO;
 
 	mutex_lock(&bdevp->bd_mutex);
 	mutex_lock_nested(&bdev->bd_mutex, 1);